a buddy of mine used cheap cloth to map out his mold on the bottom of his floorboard using the resin. then he used the mold outside the car to build the box. he said this way there is less exposure to fiberglass in getting all over you car. plus he said the cloth is easier to manipulate in tight areas. i believe he said he used a sweatshirt type cloth due to its thickness. it was his first time messing with fiber glass, but it sounded like a good idea.

If it were me I would make the bottom out of fibreglass as you intended and make the rest out od mdf, once it is all made just fibreglass the 2 halves together on the inside and presto, you have a molded box.
Once this has been done you could line the inside of the bottom with a damping material such as dynamat....

And as others have said be careful with the fibres as they aren't real good for you, wear gloves etc

Originally posted by theChris fiberglass has been used exensively in car audio. here are the key points:
1.) use a laminating resin. general purpose and finishing resins often have short working times and a wax compond included. the wax dries nice and glossy, but new fiberglass layers will not bond to it. an iso resin is ideal becuase it has more tolerance to heat.

Can one use general purpose or finishing resins and sand the hardened surfaces between fiberglass layers?

Does fiberglass bond/react well with rigid foam (insulation)?

I either want build some home speakers using some rigid foam sandwiched between a few fiberglass layers on each side or I will have to construct some sort of honeycomb sandwich between the fiberglass layers, which will be harder. Which is a better idea?

Regular styrofoam and an epoxy resin is fine, and will make something lightweight and strong. Polyester resin will probably melt the styrofoam, but it does depend on the foam composition. I'd test it before doing a lot of building.

Oh, and whichever one will melt the styrofoam from heat if you mix in too much hardener.

Corrugated cardboard would be fairly safe as a medium, and come out reasonably rigid. The fibreglass itself will be fine if you make enough layers of it though, take up less time, and be easier to work with.

I made an MDF frame for my subwoofer enclosures, then moulded aluminum oven tray liners to be the outside of the enclosure. I laid the fibreglass in that, then when it was done, peeled the aluminium off, leaving me with a very nice fibreglass surface.

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There are 10 types of people in the world. Those who understand binary, and those who don't.

Can one use general purpose or finishing resins and sand the hardened surfaces between fiberglass layers?

Finishing resin (polyester) has a wax included that rises to the surface during cure. This would have to be stripped and then the polyester surface sanded for maximum adhesion. Sanding the waxed surface would grind some of the wax into the surface.

Laminating resin is best for polyester lay-ups, since it is made for making decent bonds between new and partially cured layers. Fully cured layers need to be sanded before additional layers are added, if you want maximum available strength.

Be warned that MEK, the common catalyst for curing polyester resin, can cause blindness if splashed into the eye. Take no chances.

Epoxy helps mediate some of the layup concerns, and can develop full bond strength between layers that aren't laminated at the same time. Existing layers in the 'green cure' stage will fully bond with additional layers. They are easily trimmed with a sharp razor knife at that time as well.

Be warned skin becomes sensitized to epoxy resin with exposure. At the point when tolerance is exhausted, it will cause an intense allergic reaction. Once this happens, exposure to even tiny amounts of epoxy can cause the reaction to reoccur. The amount of exposure required to cause this is unique to individual biology. It can happen the first time you mess with it, or the millionth time.

If you want to use epoxy, wear gloves and don't take my pitiful explanation as the only truth -read up on the warnings. If you can't find any info, email me and I'll find some links.